Microemulsion oil recovery process



March 19, 1968 c. E. COOKE, JR 3,373,809

MICROEMULSION OIL RECOVERY PROCESS Filed Nov. 15, 1965 2 Sheets-Sheet 1DETERGENT ALCOHOL a (a POLAR ORGANIC) DETERGENT l PHASE T T Xmz OIL O.lN NuCI TOLUENE ZIw FIG. 1 HQ- 2 ALCOHOL 8T ALCOHOL 8| DETERGENTDETERGENT DISTILLED WATER TOLUENE OEI N NuCl TOLUENE Fla-3 CLAUDE E.COOKE,JR. INVENTOR.

ATTORNEY March 19, 1968 Filed Nov. 15, 1965 c. E. COOKE, JR

MIGROEMULSIQN OIL RECOVERY PROCESS no nnpgsagwaa 18d paonpoJ "0 FluidInjected After Water Flood, pore volumes 2 Sheets-Sheet 2 if? "if .5

CLAUDE E. COOKE,JR. INVENTOR- ATTORNEY United States Patent 3,373,809MICROEMULSION OIL RECOVERY PROCESS Claude E. Cooke, Jr., Houston, Tex.,assignor to Esso Production Research Company, a corporation of DelawareFiled Nov. 15, 1965, Ser. No. 507,836 Claims. (Cl. 166-9) ABSTRACT OFTHE DISCLOSURE In the recovery of oil from subterranean oil-bearingformations, an aqueous detergent solution is injected for the in situformation of a water external microemu sion on contacting the reservoiroil. The concentration of surfactant in the injected solution is greaterthan the minimum miscibility concentration.

This invention relates to the recovery of additional oil from poroussubterranean reservoirs. A method is provided which involves adisplacement of the reservoir oil by a concentrated aqueous detergentsolution. The detergent is selected from a limited class of materialswhich have the unique ability to solubilize unusually large amounts ofoil, forming microemulsions. In accordance with a more limitedembodiment, the addition of a polar organic compound, an alcohol forexample, is essential to the formation of a microemulsion. Such polarmaterials may be introduced with the detergent solution, or as aseparate bank.

Numerous prior disclosures have proposed the recovery of oil bydisplacement with an aqueous detergent solution. It has been a generalpremise of such prior disclosures that the essential function of adetergent is to lower the interfa-cial tension between the aqueous andoil phases. It is well known that surfactant concentrations in excess ofthe critical micelle concentration have a negligible effect oninterfacial tension. Accordingly, since the critical micelleconcentration of a detergent rarely exceeds 1 to 2 percent, theinvestigation of more concentrated detergent solutions may have appearedto hold little promise.

Of course, the solubilization of oil in aqueous solutions can occur, toan appreciable extent, in any aqueous solution of a surface-activechemical, to an appreciable extent, in any aqueous solution of asurface-active chemical, whenever micelles are formed. But the amount ofoil solubilized by a surfactant solution is usually small, because themicelles are very small, consisting of about seventy molecules ofsurfactant, for example. In most instances, an increased concentrationof surfactant is ineffective to increase the size of individualmicelles. Thus, increased concentrations of surface-active agents areusually ineffective to improve the etficiency with which residual oil isdisplaced from a porous reservoir.

Under certain conditions, however, with selected surfactants, themicelles can be caused to grow to much larger dimensions, with aconsequent increase in the amount of oil solubilized by a given amountof detergent. These systems, which include unusually large micelles andlarge amounts of solubilized oil in aqueous media, are transparent, andare known as microemulsions. It has now been found that an aqueousdetergent solution capable of forming a microemulsion with oil has anunusually high displacement efiiciency in the recovery of reservoir oil.

SUMMARY OF THE INVENTION This invention is a method for misciblydisplacing the oil contained in subterranean reservoir by injecting asolution capable of forming a water external microemul- 3,373,809Patented Mar. 19, 1968 sion with the reservoir oil upon injection. Thesolution capable of forming a water external microemulsion which willmaintain miscibility with the resident oil and following flood waterconsists of an aqueous solution of detergent and in most instances anorganic polar compound. The concentration of detergent and organic polarcompound in the aqueous solution is at or above the mini mum miscibilityconcentraiton. The minimum miscibility concentration is discussed ingreater detail hereinafter.

With few exceptions, the formation of a microemulsion requires thepresence of an organic polar material, such as an alcohol, phenol,amine, acid, etc., in addition to the surfactant or detergent itself. Itis known to displace reservoir oil with a bank of an oil-miscibleliquid, for example, wit-h alcohol alone, whereby a true molecularsolution of the reservoir oil is formed. The microemulsion-formingsolutions of the present invention are as effective as alcohol alone intheir ability to recover oil, while possessing the distinct advantage ofbeing far. less expensive. Frequently, the solutions of the presentinvention are even more effective than an oil-miscible solvent, forexample, an alcohol bank injected by itself, because relatively smallvolumes of connate water are sufficient to cause a separation of phaseswhen flooding with an alcohol alone, Whereas the solutions of thepresent invention retain their oil-miscible character despitesubstantial dilution by connate water or brine.

In accordance with one embodiment of the invention, the detergentsolution consists essentially of detergent plus water, and is injectedinto the petroleum reservoir as the sole flooding medium. However, thiswill be recognized by those skilled in the art as an uneconomicalternative compared with the injection of a detergent solution in alimited amount, sufficient to form a bank of 3 to 20 percent of thereservoir pore volume, followed by the injection of a propelling medium,usually water.

In accordance with a further embodiment of the invention, a bank ofconcentrated microemulsion-forming detergent solution is injected,followed by the injection of water containing a thickening agent such aspolyacrylamide or sulfonated polystyrene. The use of water thickened toa viscosity at least as great as the viscosity of the detergent solutionas a propelling medium is particularly preferred. The thickened waterpermits the use of a minimum detergent solution bank size, since theviscous propelling medium does not finger through the detergent bankwith a consequent disruption and dissipation of the detergent bank.

In accordance with a further embodiment of the invention, themicroemulsion-forming detergent solution is preceded by a bank of oil.In some instances, a leading bank of oil is essential to the economicsuccess of the process, particularly where the reservoir oil is highlyresistant to the formation of a microemulsion. Thus, the injected bankof oil is selected for the ease with which it forms a microemulsion,thereby permitting the detergent bank to achieve a miscible-likedisplacement. As before, the detergent bank may be followed by thickenedwater as a propelling medium.

In accordance with a further embodiment of the invention, themicroemulsion-forming detergent bank consists essentially of water, adetergent, and an organic polar compound. The aqueous detergent bankcontaining a polar additive is injected as a leading bank, or ispreceded by a bank of oil as before. The detergent bank is then followedby Water as a propelling medium, which preferably is thickened to aviscosity at least as great as that of the detergent solution.

In accordance with a still further embodiment of the invention, theorganic polar material may be injected as a separate bank, either beforeor after the injection of the aqueous detergent solution. Thisembodiment may therefore involve the successive injection of fourmatrials; that is, a leading bank of oil selected for the ease withwhich it forms a microemulsion, followed by a bank of organic polarsolvent, followed by the aqueous microemulsion-forming detergentsolution, followed by thickened water to propel the system through thereservoir.

FIGURE 1 is a ternary phase diagram illustrating the phase behaviorrequired to obtain a miscible displacement of reservoir oil.

FIGURE 2 is a ternary phase diagram showing the two-phase envelopes forvarious alcoholic detergent-brinetoluene systems.

FIGURE 3 is a ternary phase diagram showing the two-phase envelope ofthe alcoholic sodium dodecylbenzene sulfonate-water-toluene system.

FIGURE 4 is a ternary phase diagram showing the two-phase envelopes oftwo alcoholic sodium dodecylbenzene sulfonate-brine-toluene systemshaving different ratios of detergent to alcohol.

FIGURE 5 is a recovery curve obtained by displacing waterflood residualoil from a Berea sandstone core with a microemulsion-forming alcoholdetergent solution in distilled water.

The flow behavior in a porous reservoir during a microemulsion flood issimilar to the flow behavior obtained in the displacement of oil with anoil-water mutual solvent, alone, such as butyl alcohol. The flowbehavior is similar, in that the microemulsion-forming flood mediumcontains in aqueous solution certain materials which, by mass transfer,pass into the oil phase thereby swelling the residual oil, such asoccurs during an alcohol flood. In addition, some oil will become mobilebecause of a lowering of interfacial tension; and this oil is pushedahead of the microemulsion-forming solution. The oil phase left immobilein the rock is finally dissolved in or becomes miscible with theinjected fluid and begins moving at the same velocity as the injectedfluid.

It is preferred that a microemulsion flood behave as a miscibledisplacement, in order that on a pore volume basis much smaller, moreeconomical banks of injected solution can be employed to obtain high oilrecovery, than would otherwise be possible. The required conditions fora miscible displacement are illustrated by the ternary phase diagram ofFIGURE 1. It can be shown that a miscible displacement will occur if theinjected aqueous detergent solution is richer in detergent than thecomposition denoted by point C. The point C is defined by theintersection of a line drawn tangent to the two-phase envelope, at theplait point, wtih the water-detergent side of the diagram. Thisdetergent-polar organic compound concentration is referred to herein,for the purpose of convenience in nomenclature, as the MinimumMiscibility Concentration.

In those embodiments wherein the aqueous detergent solution alsocontains a polar organic compound, such as an alcohol, it has been foundconvenient to approximate the phase behavior of the resultingfour-component system in a ternary diagram, by treating the polarsolvent and detergent as a single component. This representation isexact only when the ratio of polar compound to detergent is the same inboth phases of any two-phase composition. The error introduced by thisassumption is relatively slight, however, and can readily be toleratedin preference to the complexity of a three dimensional fourcomponentphase model. Thus, in FIGURE 1, the vertex designated detergent mayrepresent a certain fixed ratio of detergent to polar additive. In suchinstances, the point C as defined above represents the minimumconcentration of detergent plus polar additive, in water, required toachieve miscible displacement of the oil.

Accordingly, for the purposes of the present invention, the preferredembodiments are those characterized by a ternary-phase diagram having alarge one-phase region. Systems having a large one-phase region arepreferred, since the point C for such system falls closer to t Watervertex of the ternary diagram, which means that miscible displacementmay be achieved with lower concentrations of detergent, or detergentplus polar additive. It is essential that the two-phase envelope fallentirely below that level of the ternary diagram which corresponds to70% detergent, or 70% detergent plus polar organic compound. Preferably,the two-phase region should not include any compositions which containmore than 50% detergent, or 50% detergent plus polar organic.

In accordance with a more limited aspect of the invention, the two-phaseregion may be further reduced in size, not only by the selection ofvarious preferred species of detergent and polar additive, but also byfirst injecting an oil component charcterized by the formation ofmicroemulsion solutions with unusual ease. This is accomplished, forexample, by injecting a small bank of toluene or other light aromatic orparafiinic oil; or any material which is miscible with the crude andmore readily capable of forming microemulsion solutions than is thereservoir crude.

Suitable examples of polar organic compounds for use in accordance withthe invention include the n-, cycloand iso-alcohols having 4-16 carbonatoms per molecule; the n-, cycloand iso-amines having 5-12 carbon atomsper molecule; phenol and phenols having side chains with 1-10 carbonatoms per molecule; n-, cycloand isomercaptans having 2-10 carbon atomsper molecule; glycols having 2-12 carbon atoms per molecule; fatty acidshaving 6-22 carbon atoms per molecule; glycerols having 3-18 carbonatoms per molecule; ketones having 5-18 carbon atoms per molecule;ethers having 418 carbon atoms per molecule; aldehydes having 418 carbonatoms per molecule; and mixtures of two or more of the above. All thesemolecules may contain saturated or unsaturated carbon-carbon bonds.

Suitable concentrations of polar organic compound, in those embodimentsof the invention which comprise the injection of both detergent andpolar organic in the same bank, range from about 15% to 60% by weight,preferably from 20% to 40% by weight, depending primarily upon theselection of detergent, and the relative ease with which the reservoiroil or injected oil forms microemulsions. As noted earlier, the polarorganic may be injected in a separate bank, or in highly concentratedbanks. The stated range of concentrations would apply, in that event, tothe effective concentration of polar organic, when considering thecombination of the detergent bank plus the polar organic-comprisingbank.

Suitable detergents or surfactants include anionic and nonioniccompounds, for example, sulfon-ated aromatic hydrocarbons, ethyleneoxide condensates of aliphatic acids, alkyl aryl polyalkylene glycolethers, esters of sulfosuccinic acid, monoand dibasic carboxylic acids,alkyl and aryl sulfates; specific examples of which include isopropylnaphthalene sodium sulfonate, sulfonated petroleum distillates, ethyleneoxide condensates of coco fatty acids, octylphenyl polyoxyethyleneether, diisoctyl sodium sulfosuccinate, perfluocaprylic acid, diisohexylsuccinic acid, dodecyl sulfate and amylphenyl sulfate.

The concentrations of detergent(s) useful in accordance with the presentinvention range from about 5% by weight up to about 40% by weight, andpreferably from 10% to 30% by weight, based on the total weight of theinjected detergent solution, which usually includes the polar organiccompound. It will be apparent that these concentrations are much greaterthan the concentrations proposed in the prior art for the use ofsurfactants as waterfiood additives in oil recovery processes. Thegreater concentrations are essential in accordance with the presentinvention, since the present mechanism involves microemulsion formationand miscible displacement, whereas the prior art use of detergents hasbeen to lower interfacial tension, without achieving miscibility.

Specific combinations of a polar organic compound and a soap ordetergent for use in the present invention include phenol and sodiumoleate; phenol and sodium abietate; phenol and ethanolamine oleate; pineoil and sodium oleate; glycerol and turkey red oil; diethylene glycoland turkey red oil; octyl alcohol and potassium myristate; octylamineand potassium myristate; octylamine and potassium myristate; octylmercaptan and potassium myristate; cetyl alcohol and oleic acid;p-methyl cyclohexanol and oleic acid; oleic acid and sodium oleate;namyl alcohol and an octylphenyl polyoxyethylene ether obtained byreacting 13 mols ethylene oxide with octylphenol (Triton X-102).

It will be apparent that some of the above-named detergents aresensitive to divalent ions, such as calcium and magnesium, frequentlyencountered in petroleum reservoirs. It is contemplated in suchinstances that the detrimental effect of these ions can be avoided bythe addition of a chelating agent to the flood water, or by prefloodingthe reservoir to displace divalent salt-containing brines and therebyeliminate the problem.

In FIGURE 2, each two-phase envelope was obtained with a differentalcohol. Envelope 1 was obtained with tertiary amyl alcohol; envelope 2was obtained with normal butyl alcohol; envelope 3 was obtained withcresol; envelope 4 was obtained with normal amyl alcohol; and envelope 5was obtained with normal hexyl alcohol. The detergent in each instancewas sodium dodecyl benzene sulfonate. The ratio of sulfonate to alcoholwas 2:1 by weight in each system. In the order named, these polaradditives have a decreasing solubility in water. It is signif icant thatfor these materials, the lower the water solu' bility of the polaradditive, the larger is the one-phase region of the diagram; andconsequently, the greater is the solubilizing power of themicroemulsion-forming solution. For example, miscible displacement canbe achieved with a lower concentration of the normal hexylalcoholdetergent combination, than with similar combinations ofdetergent and the lower molecular weight alcohols or cresol.

In certain instances, gel formation may tend to occur when concentratedsolutions of detergent are prepared, with or without the presence ofpolar organic solvent and/or oil. Therefore, it is generally advisableto test a proposed detergent solution, in contact with the reservoiroil, prior to injection, in order to determine its suitability as adisplacing medium. A viscosity in excess of 200 cps. is considered toogreat for most flooding operations, due to low injectivities at theinput wells, and the consequently excessive periods of time required tocomplete the recovery of oil. Ordinarily, the solutions injected inaccordance with the invention have a viscosity of about cps., andpreferably should not exceed 100 cps.

In FIG. 3, the detergent is sodium dodecylbenzene sulfonate, and thealcohol is normal butanol. A weight ratio of sulfonate to butanol of 1:1has been found to give esentially the same two-phase envelope asobtained with a sulfonate-to-butanol ratio of 0.838:1. The two-phaseregion for this system is unusually small, indicating that a successfulmiscible displacement can be obtained with an unusually high proportionof water in the microemulsion-forming flood bank.

The system of FIGURE 4 differs from that of FIG- URE 3 only in thesubstitution of 0.1 N sodium chloride for distilled water. Curve I isthe two-phase envelope for a sulfonate-to-butanol ratio of 0.838z1,whereas curve II is the two-phase envelope obtained for a weight ratioof sulfonate-to-butanol of 1:1. Thus, the presence of salt decreases theamount of solubilized toluene; and the amount solubilized increases withan increasing ratio of sulfonate to alcohol.

The recovery curve of FIGURE 5 illustrates the results of Example Ibelow.

Example I A 3-ft.-long, 2-in.-diameter Berea sandstone core was preparedto contain water and 32% pore volume of residual oil after a Waterfiood.A solution consisting of 16.1% dodecylbenzene sulfonic acid neutralizedwith NaOH, and 27.3% n-butyl alcohol in distilled water was theninjected into the core. A total of 46.7% pore volume of solution wasinjected, at a linear flow rate of one foot per day. This solution wasfollowed by a water solution of polyacrylamide, a polymer used toincrease the viscosity of the flood water to approximately the viscosityof the microemulsion-forming sulfonate-alcohol water solution (6.5cps.). This was done to prevent fingering or channeling of water throughthe microemulsion solution. The effluent from the column was collectedin several steps, and the microemulsion was broken by the addition ofmethanol so that the oil content could be measured. About of theresidual oil was produced before breakthrough of the detergent. Thetotal recovery was 97% of the residual oil after the injection of about1.5 pore volumes of fluid.

Example 11 A petroleum reservoir is waterflooded to a residual crude oilsaturation of about 30% pore volume. In accordance with the presentinvention, flood water is then injected which contains 20% by weightpetroleum sulfonates, and 30% by weight oxygenated olefinichydrocarbons. The petroleum sulfonates are obtained, for example, bytreating a heavy aromatic naphtha (average mol. weight of 230) with 20%oleum, separating the acid layer which contains water-solublesulfonates, and neutralizing with NaOH to obtain the correspondingsodium salts. The oxygenated hydrocarbons are obtained, for example, bythe partial oxidation or oxygenation of unsaturated hydrocarbonfractions, in accordance with known methods. The olefins present in suchfractions are thereby converted to aldehydes, alcohols, ethers, ketones,and minor amounts of other oxygen compounds. Such reaction productmixtures are particularly suited for use in accordance with theinvention, without the need for separation or refinement, which affordsan attractive economy with respect to sources of relatively purecompounds.

The solution of petroleum sulfonates and oxygenated hydrocarbons isinjected until about 0.05 pore volume of the reservoir is flooded.Thereafter, a 0.2 pore volume bank of thickened Water is injected,containing 0.05% by weight of partially hydrolyzed polyacrylamide as thethickener. The thickened bank is then followed with water or brine untila total of about 1.5 pore volumes of flooding medium is injected,counting the detergent-polar organic bank and the thickened water. Oilrecovery is essentially complete, indicating miscible displacement.

Example 111 A series of aqueous solutions containing 1.5 parts by weightof petroleum sulfonate detergent, and one part by weight of n-pentanol,were prepared. The ability of each solution to solubilize oil wasdetermined by slowly adding a petroleum crude oil, while stirring themixture, until the first appearance of turbidity was noted. Thefollowing data were obtained:

Wt. percent detergent plus Wt. percent oil alcohol in total system:solubilized 24.0 4.9 28.0 5.5 42.5 14.6 45.0 27.2

It is readily seen from the data that this combination of detergent andalcohol falls within the preferred scope of the invention, since thesystem containing detergent plus alcohol and substantially equal weightsof water and oil was on the boundary between the one-phase and thetwo-phase parts of the phase diagram. The two-phase envelope fallsentirely below that part of the phase diaram which corresponds to 45.0%detergent plus polar organic.

What is claimed is:

1. A method for the recovery of oil from a porous reservoir having aninput well and an output well which comprises injecting through saidinput well a detergent solution capable of forming a water-externalmicroemulsion with oil, forming a water-external microemulsion withinthe reservoir, and Withdrawing displaced reservoir oil from said outputwell, wherein the concentration of the detergent is at least the minimummiscibility concentration which is a detergent concentration denoted ona water and detergent side of a water, oil, and detergent ternary phasediagram by an intersection of the water and detergent side with a linetangent to a phase envelope at a plait point.

2. The method as defined by claim 1 wherein the amount of detergentsolution injected is 3 percent to 20 percent of the pore volume of thereservoir flooded.

3. The method as defined by claim 1 wherein the detergent is selectedfrom the group consisting of sulfonated aromatic hydrocarbons, ethyleneoxide condensates of aliphatic acids, alkyl aryl polyalkylene glycolethers, esters of sulfosuccinic acid, monoand dibasic carboxylic acids,alkyl and aryl sulfates.

4. The method as defined by claim 1 further including injecting a lighthydrocarbon solvent, miscible with the reservoir oil prior to injectionof the detergent solution.

5. The method as defined by claim 1 further including injecting a polarorganic material as a separate bank.

6. A method for the recovery of oil from a porous subterranean reservoirhaving an input well and an output well which comprises injectingthrough said input well a solution capable of forming a water-externalmicroemulsion on contacting oil, forming a water-external microemulsionin the reservoir, and withdrawing displaced reservoir oil from saidoutput well wherein the solution comprises dgt ergent and polar organicmaterial in aqueous solution, the concentration of detergent and polarorganic material being at least the minimum miscibility concentrationwhich is a detergent-polar organic material concentration denoted on awater and detergentpolar organic material side of a water, oil, anddetergentpolar organic material ternary phase diagram by an intersectionof the water and detergent-polar organic material side with a linetangent to a phase envelope at a plait point.

7. The method as defined in claim 4 wherein the amount of the aqueoussolution of detergent and polar organic material injected is 3 percentto 20 percent of the pore volume of the reservoir flooded.

8. The method as defined in claim 4 wherein the detergent is selectedfrom the group consisting of sulfonated aromatic hydrocarbons, ethyleneoxide condensates of aliphatic acids, alkyl aryl polyalkylene glycolethers, esters of sulfosuccinic acid, monoand dibasic carboxylic acids,alkyl and aryl sulfates.

9. The method as defined in claim 4 wherein the polar organic compoundis selected from the group consisting of normal, cycloand iso-alcoholshaving 416 carbon atoms per molecule; the n-, cycloand iso-amines having5-12 carbon atoms per molecule; phenol and phenols having side chainswith 1-10 carbon atoms per molecule; n-, cycloand iso-mercaptans having210 carbon atoms per molecule; glycols having 2-12 carbon atoms permolecule; fatty acids having 6-22 carbon atoms per molecule; glycerolshaving 3-18 carbon atoms per molecule; ketones having 5-18 carbon atomsper molecule; ethers having 418 carbon atoms per molecule; aldehydeshaving 4-18 carbon atoms per molecule.

10. The method as defined by claim 5 further includt ing injecting alight hydrocarbon solvent, miscible with the reservoir oil prior toinjection of the microemulsion .1" forming solution.

References Cited UNITED STATES PATENTS 3,330,344 7/1967 Reisberg l6692,742,089 4/1956 Morse et al. 166--9 3,131,759 5/1964 Susser et al. 16693,163,214 12/1964 Csaszar 1669 3,254,714 6/1966 Gogarty et al. 16693,266,570 8/1966 Gogarty 166-9 3,275,075 9/1966 Gogarty 1669 3,301,3251/1967 Gogarty 166--9 3,307,628 3/1967 Sena 166-9 JAMES A. LEPPINK,Primary Examiner.

